Research_Update 12thNov2012

Pubblicato: novembre 16, 2012 in general

Effects of 12 weeks of block periodization on performance and performance indices in well-trained cyclists.
Rønnestad BR, Ellefsen S, Nygaard H, Zacharoff EE, Vikmoen O, Hansen J, Hallén J.
Section for Sport Science, Lillehammer University College, Lillehammer, Norway.
The purpose of this study was to compare the effects of two different methods of organizing endurance training in trained cyclists during a 12-week preparation period. One group of cyclists performed block periodization (BP; n?=?8), wherein every fourth week constituted five sessions of high-intensity aerobic training (HIT), followed by 3 weeks of one HIT session. Another group performed a more traditional organization (TRAD; n?=?7), with 12 weeks of two weekly HIT sessions. The HIT was interspersed with low-intensity training (LIT) so that similar total volumes of both HIT and LIT were performed in the two groups. BP achieved a larger relative improvement in VO(2max) than TRAD (8.8?±?5.9% vs 3.7?±?2.9%, respectively, P?<?0.05) and a tendency toward larger increase in power output at 2?mmol/L [la(-) ] (22?±?14% vs 10?±?7%, respectively, P?=?0.054). Mean effect size (ES) of the relative improvement in VO(2max) , power output at 2?mmol/L [la(-) ], hemoglobin mass, and mean power output during 40-min all-out trial revealed moderate superior effects of BP compared with TRAD training (ES range was 0.62-1.12). The present study suggests that BP of endurance training has superior effects on several endurance and performance indices compared with TRAD.
© 2012 John Wiley & Sons A/S. Published by Blackwell Publishing Ltd.

Protein supplementation augments the adaptive response of skeletal muscle to resistance-type exercise training: a meta-analysis.
Cermak NM, Res PT, de Groot LC, Saris WH, van Loon LJ.
Departments of Human Movement Sciences and Human Biology, NUTRIM School for Nutrition, Toxicology and Metabolism, Maastricht University Medical Centre+, Maastricht, Netherlands, and the Division of Human Nutrition, Wageningen University, Wageningen, Netherlands.
Protein ingestion after a single bout of resistance-type exercise stimulates net muscle protein accretion during acute postexercise recovery. Consequently, it is generally accepted that protein supplementation is required to maximize the adaptive response of the skeletal muscle to prolonged resistance-type exercise training. However, there is much discrepancy in the literature regarding the proposed benefits of protein supplementation during prolonged resistance-type exercise training in younger and older populations.
The objective of the study was to define the efficacy of protein supplementation to augment the adaptive response of the skeletal muscle to prolonged resistance-type exercise training in younger and older populations.
A systematic review of interventional evidence was performed through the use of a random-effects meta-analysis model. Data from the outcome variables fat-free mass (FFM), fat mass, type I and II muscle fiber cross-sectional area, and 1 repetition maximum (1-RM) leg press strength were collected from randomized controlled trials (RCTs) investigating the effect of dietary protein supplementation during prolonged (>6 wk) resistance-type exercise training.
Data were included from 22 RCTs that included 680 subjects. Protein supplementation showed a positive effect for FFM (weighted mean difference: 0.69 kg; 95% CI: 0.47, 0.91 kg; P < 0.00001) and 1-RM leg press strength (weighted mean difference: 13.5 kg; 95% CI: 6.4, 20.7 kg; P < 0.005) compared with a placebo after prolonged resistance-type exercise training in younger and older subjects.

Protein supplementation increases muscle mass and strength gains during prolonged resistance-type exercise training in both younger and older subjects.
Blood flow restricted exercise and vascular function.
Horiuchi M, Okita K.
Department of Physiology, Yamanashi Institute of Environmental Sciences, Kami-yoshida 5597, Fuji-yoshida, Yamanashi 4030005, Japan ; Northern Regions, Life long Sports Research Center, Hokusho University, Bunkyoudai 23, Ebetsu, Hokkaido 0698511, Japan.
It is established that regular aerobic training improves vascular function, for example, endothelium-dependent vasodilatation and arterial stiffness or compliance and thereby constitutes a preventative measure against cardiovascular disease. In contrast, high-intensity resistance training impairs vascular function, while the influence of moderate-intensity resistance training on vascular function is still controversial. However, aerobic training is insufficient to inhibit loss in muscular strength with advancing age; thus, resistance training is recommended to prevent sarcopenia. Recently, several lines of study have provided compelling data showing that exercise and training with blood flow restriction (BFR) leads to muscle hypertrophy and strength increase. As such, BFR training might be a novel means of overcoming the contradiction between aerobic and high-intensity resistance training. Although it is not enough evidence to obtain consensus about impact of BFR training on vascular function, available evidences suggested that BFR training did not change coagulation factors and arterial compliance though with inconsistence results in endothelial function. This paper is a review of the literature on the impact of BFR exercise and training on vascular function, such as endothelial function, arterial compliance, or other potential factors in comparison with those of aerobic and resistance training.

Brain Reorganization following Weight Loss.
Rosenbaum M, Leibel RL.
Division of Molecular Genetics, Department of Pediatrics, College of Physicians and Surgeons, Columbia University, New York, NY, USA.
The long-term stability of bodyweight despite wide variation in energy intake and expenditure suggests that at usual weight energy intake and output are ‘coupled’ to maintain body energy stores. Our model for some of the molecular mechanics of this regulation of energy stores is based on the concept of a neurally encoded ‘threshold’ for minimum body fat, below which compensatory physiology is invoked to restore body fat. The existence of such a centrally encoded threshold is supported by the similarities in response to maintenance of a reduced weight between lean and obese individuals, and the tendency for weight-reduced individuals to regain weight to levels of fat stores similar to those present prior to initial weight loss. Brain responses to food and the observed changes in energy expenditure that occur during maintenance of a reduced weight are largely reversed by the administration of the adipocyte-derived hormone, leptin. Copyright © 2012 Nestec Ltd., Vevey/S. Karger AG, Basel.

Dietary intakes of carbohydrates in relation to prostate cancer risk: a prospective study in the Malmo Diet and Cancer cohort.
Drake I, Sonestedt E, Gullberg B, Ahlgren G, Bjartell A, Wallström P, Wirfält E.
Research Group in Nutritional Epidemiology, Department of Clinical Sciences in Malmö, Lund University, Malmö, Sweden, and the Department of Urology, Skåne University Hospital, Malmö, Sweden.
Dietary carbohydrates have been implicated in relation to prostate cancer.
Our objective was to examine the associations between dietary intakes of carbohydrates, fiber, and their food sources and risk of prostate cancer, overall and by case severity, in the Malmö Diet and Cancer cohort.
The analysis included 8128 men aged 45-73 y without a history of cancer, cardiovascular disease, or diabetes and who were classified as adequate energy reporters. After a median follow-up time of 15 y, prostate cancer was diagnosed in 817 men. We used Cox proportional hazards regression to model associations between energy-adjusted nutrient and food intakes with risk of incident prostate cancer, with competing risk of death from non-prostate cancer causes taken into account.
After adjustment for age and other known or potential risk factors, we observed no associations between total carbohydrates or dietary fiber and prostate cancer. We observed positive associations between the intake of low-fiber cereals with overall and low-risk prostate cancer and between intakes of cake and biscuits and rice and pasta with low-risk prostate cancer (all P-trend < 0.05). A high intake compared with zero consumption of sugar-sweetened beverages was associated with increased risk of symptomatic prostate cancer (HR: 1.38; 95% CI: 1.04, 1.84).
Results from this large study with high-validity dietary data suggest that a high intake of refined carbohydrates may be associated with increased risk of prostate cancer. However we observed no significant associations with high-risk prostate cancer, and not all foods that are typically high in refined carbohydrates were associated with prostate cancer.

[Carbohydrate sweeteners and obesity].
[Article in Polish]
Wystrychowski G, Zukowska-Szczechowska E, Obuchowicz E, Grzeszczak W, Wystrychowski A.
Katedra i Klinika Chorób Wewnetrznych, Diabetologii i Nefrologii SaIskiego Uniwersytetu Medycznego w Katowicach.
The U.S. prevalence of obesity increases since the mid-70s of the 20th century. Around that time high-fructose corn syrup (HFCS)–mixture of fructose and glucose was introduced as a sweetener replacing sucrose in the food production. HFCS containing 55% fructose and 42-45% glucose (HFCS55) has dominated the American soft drink industry and HFCS has recently become commonly used in Poland. The coincidence of HFCS introduction and obesity epidemic raised widely publicized suspicions of a causal relationship between the two. As a possible mechanism, a higher content of fructose in the HFCS55, as compared with sucrose was suggested -fructose is known to increase serum uric acid level, induce hepatic lipogenesis and not stimulate postprandial hyperinsulinemia, a main activator of leptin release. Few comparative studies of HFCS and sucrose have largely failed to reveal any different impacts on the metabolic parameters, yet they were mainly short-term. It has been recently shown that obesity is linked with changes in the intenstinal flora. Among the causes of allegedly different effects of sucrose and HFCS on metabolism, their influence on the gut microbiome has not been examined. Some bacterial types do not hydrolyze sucrose which may determine different compositions of gut flora with the use of both sweeteners. Studies involving quantitative analysis of bacterial DNA in the stool, both in animals and in humans, shall shed light on the issue that has recently so much absorbed the U.S. public opinion.
[PubMed – indexed for MEDLINE]

Effects of high-fructose corn syrup and sucrose consumption on circulating glucose, insulin, leptin, and ghrelin and on appetite in normal-weight women.
Melanson KJ, Zukley L, Lowndes J, Nguyen V, Angelopoulos TJ, Rippe JM.
Department of Nutrition and Food Sciences, University of Rhode Island, Kingston, Rhode Island, USA.
Fructose has been implicated in obesity, partly due to lack of insulin-mediated leptin stimulation and ghrelin suppression. Most work has examined effects of pure fructose, rather than high-fructose corn syrup (HFCS), the most commonly consumed form of fructose. This study examined effects of beverages sweetened with HFCS or sucrose (Suc), when consumed with mixed meals, on blood glucose, insulin, leptin, ghrelin, and appetite.
Thirty lean women were studied on two randomized 2-d visits during which HFCS- and Suc-sweetened beverages were consumed as 30% of energy on isocaloric diets during day 1 while blood was sampled. On day 2, food was eaten ad libitum. Subjects rated appetite at designated times throughout visits.
No significant differences between the two sweeteners were seen in fasting plasma glucose, insulin, leptin, and ghrelin (P > 0.05). The within-day variation in all four items was not different between the two visits (P > 0.05). Net areas under the curve were similar for glucose, insulin, and leptin (P > 0.05). There were no differences in energy or macronutrient intake on day 2. The only appetite variable that differed between sweeteners was desire to eat, which had a higher area under the curve the day after Suc compared with HFCS.
These short-term results suggest that, when fructose is consumed in the form of HFCS, the measured metabolic responses do not differ from Suc in lean women. Further research is required to examine appetite responses and to determine if these findings hold true for obese individuals, males, or longer periods.



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